Hermetic refrigerant compressor and refrigerator-freezer using the same

ABSTRACT

In a hermetic refrigerant compressor, a thrust bearing (e.g., thrust ball bearing (210)) is provided on a thrust surface (136) of a main bearing (134). One end of a sliding surface of the main bearing (134), the one end being closer to a compression chamber (133) than an opposite end of the sliding surface, is a first end, and the opposite end of the sliding surface is a second end. A distance between a center axis of the compression chamber (133) and the second end of the sliding surface (sliding surface lower end (139)) of the main bearing (134) is a distance L, and a distance between the center axis of the compression chamber (133) and the first end of the sliding surface (sliding surface upper end (138)) of the main bearing (134) is a distance La. When the distance L is in a range of 38 mm to 51 mm, the distance La is less than or equal to 16 mm.

TECHNICAL FIELD

The present invention relates to a hermetic refrigerant compressor for use in, for example, a refrigerator or an air conditioner, and also relates to a refrigerator-freezer using the hermetic refrigerant compressor.

BACKGROUND ART

In recent years, from the viewpoint of global environment conservation, the development of a high-efficient hermetic refrigerant compressor that uses less fossil fuels has been conducted. For example, in order to achieve high efficiency, it has been proposed to form various films on sliding surfaces of slide members included in the hermetic refrigerant compressor, and to use lubricating oil having a reduced viscosity.

The hermetic refrigerant compressor includes a sealed container in which the lubricating oil is stored. The sealed container also accommodates an electric element and a compression element. The compression element includes, as the slide members, for example, a crankshaft, a piston, and a connecting rod serving as a coupler. A main shaft of the crankshaft and a main bearing, the piston and a bore, a piston pin and the connecting rod, and an eccentric shaft of the crankshaft and the connecting rod, etc., form slide parts with each other.

As one example of the hermetic refrigerant compressor that uses lubricating oil having a reduced viscosity, Patent Literature 1 discloses a reciprocating compressor. In Patent Literature 1, the lubricating oil used in the reciprocating compressor has a kinematic viscosity in the range of 3 mm²/S to 10 mm²/S at 40° C.

If the lubricating oil has a low viscosity, an oil film is not easily formed by the lubricating oil. In this respect, in the reciprocating compressor (hermetic refrigerant compressor) disclosed by Patent Literature 1, the surfaces of the slide members forming the slide parts (i.e., sliding surfaces) are subjected to special treatment to facilitate the formation of the oil film, so that even in a case where lubricating oil having a low viscosity is used and the oil film formed thereby is thin, wear or seizing of the piston and the connecting rod is prevented.

Not only the use of low-viscosity lubricating oil, but also the adoption of a configuration in which a main bearing is provided with a thrust bearing is also known as one way of achieving high efficiency. For example, Patent Literature 2 discloses a hermetic compressor in which a thrust bearing is provided on a thrust surface of a main bearing. This thrust ball bearing includes; a plurality of rolling elements (e.g., balls) retained by a retainer; and an upper race and a lower race provided over and under the rolling elements, respectively. The rolling elements roll on the upper and lower races while being in point contact with these races. Accordingly, the thrust bearing functions as a rolling bearing. The rolling bearing thus configured allows the main shaft to rotate with less friction while supporting a load in a perpendicular direction. This makes it possible to effectively heighten the efficiency of the hermetic refrigerant compressor.

By heightening the efficiency of a hermetic refrigerant compressor, the energy saving of a refrigerator-freezer using the hermetic refrigerant compressor can be realized. Other than heightening the efficiency of the hermetic refrigerant compressor, there is also another known way of achieving energy saving of the refrigerator-freezer, which is to lower the operation speed of the hermetic refrigerant compressor. There has been a proposed hermetic refrigerant compressor configuration that can be made suited for low-speed operation.

For example, Patent Literature 3 discloses a compressor (hermetic refrigerant compressor) configured such that the thickness of a flange that radially protrudes between a main shaft and an eccentric shaft of a crankshaft is set to 4 mm or less so as to avoid decrease in the amount of lubricating oil fed between a cylinder and a piston during low-speed operation. Accordingly, the position of the entire cylinder can be lowered without reducing the cross-sectional area of the cylinder. As a result, the lubricating oil more easily reaches the upper surface of the piston, and thereby the amount of lubricating oil fed between the cylinder and the piston can be increased.

CITATION LIST Patent Literature

PTL 1: Japanese Patent No. 5222244

PTL 2: Japanese Patent No. 6469575

PTL 3: Japanese Laid-Open Patent Application Publication No. 2018-035727

SUMMARY OF INVENTION Technical Problem

The efficiency of hermetic refrigerant compressors has been heightened more and more in recent years. By providing the main bearing with the thrust bearing as in Patent Literature 2, the efficiency of the hermetic refrigerant compressor can be further heightened. In this case, however, due to the presence of the thrust bearing, the overall height of the hermetic refrigerant compressor increases. If such a hermetic refrigerant compressor is installed in a refrigerator-freezer, the size of a machinery room in the refrigerator-freezer needs to be increased, which results in reduction in the internal volume of the refrigerator-freezer.

As a prior art example for avoiding such increase in the overall height of the hermetic refrigerant compressor, Patent Literature 2 discloses an example in which the wall thickness of a support portion of a cylinder block is reduced. Regarding this prior art example, Patent Literature 2 points out a technical problem in that when the wall thickness of the support portion of the cylinder block is reduced, the stiffness of the cylinder block is reduced, and consequently, the main bearing tends to be deformed easily. In light of this, Patent Literature 2 adopts a configuration that makes it possible to avoid increase in the overall height without reducing the wall thickness of the support portion.

Meanwhile, in Patent Literature 3, as described above, the thickness of the flange that is positioned between the main shaft and the eccentric shaft of the crankshaft is made thin, specifically, 4 mm or less, so as to avoid increase in the overall height. However, if the thickness of the flange is made excessively thin, it causes inclination of the eccentric shaft relative to the main shaft. Each of Patent Literature 2 and Patent Literature 3 describes that if the entire crankshaft is inclined in the main bearing, the heightening of the efficiency of the compressor is hindered. However, none of the patent literatures takes inclination of the eccentric shaft relative to the main shaft into consideration.

By using low-viscosity lubricating oil as in Patent Literature 1, a frictional coefficient between slide members forming a slide part is reduced, and thereby high efficiency can be achieved. In this case, however, there is a risk of causing reduction in the wear resistance of the slide part. In Patent Literature 1, as described above, the sliding surfaces are subjected to special treatment to avoid reduction in the wear resistance. However, performing the special treatment causes increase in the manufacturing cost.

The present invention has been made to solve the above-described problems. An object of the present invention is to provide a hermetic refrigerant compressor including a thrust bearing, the hermetic refrigerant compressor making it possible to achieve high efficiency without requiring special treatment on sliding surfaces and to avoid increase in the overall height without making the flange excessively thin.

Solution to Problem

In order to solve the above-described problems, a hermetic refrigerant compressor according to the present invention includes a sealed container in which lubricating oil is stored, the sealed container accommodating an electric element and a compression element, the compression element being driven by the electric element and configured to compress a refrigerant. The compression element includes: a crankshaft including a main shaft and an eccentric shaft; a cylinder block including a compression chamber; a piston that is inserted in the compression chamber in a reciprocable manner; a coupler that couples the piston and the eccentric shaft; a main bearing that pivotally supports the main shaft; and a thrust bearing provided on a thrust surface of the main bearing. One end of a sliding surface of the main bearing, the one end being closer to the compression chamber than an opposite end of the sliding surface, is a first end. The opposite end of the sliding surface is a second end. A distance between a center axis of the compression chamber and the second end of the sliding surface of the main bearing is a distance L. A distance between the center axis of the compression chamber and the first end of the sliding surface of the main bearing is a distance La. When the distance L is in a range of 38 mm to 51 mm, the distance La is less than or equal to 16 mm.

According to the above configuration, in the hermetic refrigerant compressor including the thrust bearing, when the distance L, which affects the overall height of the hermetic refrigerant compressor, is specified within a predetermined range, the upper limit of the distance La between the center axis of the compression chamber and the first end of the sliding surface of the main bearing is specified to 16 mm. This makes it possible to avoid increase in the overall height of the hermetic refrigerant compressor without making a flange excessively thin, the flange contributing to the stability of the eccentric shaft, and also makes it possible to reduce the load on the main shaft without subjecting sliding surfaces to special treatment. Consequently, the efficiency of the hermetic refrigerant compressor can be further heightened without increasing the overall height of the hermetic refrigerant compressor. In addition, since the flange is not made excessively thin, not only high efficiency but also favorable reliability of the hermetic refrigerant compressor can be achieved.

A refrigerator-freezer according to the present invention includes a refrigerant circuit including: the hermetic refrigerant compressor configured as above; a radiator; a decompressor; and a heat absorber. In the refrigerant circuit, the hermetic refrigerant compressor, the radiator, the decompressor, and the heat absorber are connected by piping in an annular manner.

The above configuration makes it possible to avoid increase in the overall height of the hermetic refrigerant compressor including the thrust bearing without making the flange thin, and also makes it possible to reduce the load on the main shaft without requiring special treatment on the sliding surfaces. Consequently, high efficiency and favorable reliability of the hermetic refrigerant compressor are achieved. By including the hermetic refrigerant compressor, which is highly efficient and has favorable reliability, in the refrigerator-freezer, the power consumption of the refrigerator-freezer can be reduced, and also, the refrigerator-freezer can be made highly reliable.

The above and other objects, features, and advantages of the present invention will more fully be apparent from the following detailed description of preferred embodiments with accompanying drawings.

Advantageous Effects of Invention

The present invention is configured as described above, and has an advantage of being able to provide a hermetic refrigerant compressor including a thrust bearing, the hermetic refrigerant compressor making it possible to achieve high efficiency without requiring special treatment on sliding surfaces and to avoid increase in the overall height without making the flange excessively thin.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view showing one example of the configuration of a hermetic refrigerant compressor according to an embodiment of the present disclosure.

FIG. 2 is a fragmentary sectional view of the hermetic refrigerant compressor shown in FIG. 1 , the view schematically showing one example of a distance L, a distance La, and a load applied to a main shaft slide part (a main shaft load) in the hermetic refrigerant compressor.

FIG. 3 is a fragmentary sectional view of the hermetic refrigerant compressor shown in FIG. 1 , the view schematically showing one configuration example of an essential part of a thrust bearing in the hermetic refrigerant compressor.

FIG. 4 is a schematic diagram showing one example of the configuration of a refrigerator-freezer including the hermetic refrigerant compressor shown in FIG. 1 .

FIG. 5 is a graph showing one example of a relationship among the distance La, the main shaft load F, and the inclination angle of an eccentric shaft in the hermetic refrigerant compressor shown in FIG. 1 .

FIG. 6A is a graph showing one example of the molecular weight distribution of lubricating oil used in the hermetic refrigerant compressor shown in FIG. 1 , and FIG. 6B is a graph showing one example of a relationship between the content of a high molecular weight component in the lubricating oil shown in FIG. 6A and the coefficient of performance of the hermetic refrigerant compressor shown in FIG. 1 .

FIG. 7 is a graph showing one example of a relationship between a rotation speed and compressor efficiency of the hermetic refrigerant compressor shown in FIG. 1 .

DESCRIPTION OF EMBODIMENTS

A hermetic refrigerant compressor according to the present disclosure includes a sealed container in which lubricating oil is stored, the sealed container accommodating an electric element and a compression element, the compression element being driven by the electric element and configured to compress a refrigerant. The compression element includes: a crankshaft including a main shaft and an eccentric shaft; a cylinder block including a compression chamber; a piston that is inserted in the compression chamber in a reciprocable manner; a coupler that couples the piston and the eccentric shaft; a main bearing that pivotally supports the main shaft; and a thrust bearing provided on a thrust surface of the main bearing. One end of a sliding surface of the main bearing, the one end being closer to the compression chamber than an opposite end of the sliding surface, is a first end. The opposite end of the sliding surface is a second end. A distance between a center axis of the compression chamber and the second end of the sliding surface of the main bearing is a distance L. A distance between the center axis of the compression chamber and the first end of the sliding surface of the main bearing is a distance La. When the distance L is in a range of 38 mm to 51 mm, the distance La is less than or equal to 16 mm.

According to the above configuration, in the hermetic refrigerant compressor including the thrust bearing, when the distance L, which affects the overall height of the hermetic refrigerant compressor, is specified within a predetermined range, the upper limit of the distance La between the center axis of the compression chamber and the first end of the sliding surface of the main bearing is specified to 16 mm. This makes it possible to avoid increase in the overall height of the hermetic refrigerant compressor without making a flange excessively thin, the flange contributing to the stability of the eccentric shaft, and also makes it possible to reduce the load on the main shaft without subjecting sliding surfaces to special treatment. Consequently, the efficiency of the hermetic refrigerant compressor can be further heightened without increasing the overall height of the hermetic refrigerant compressor. In addition, since the flange is not made excessively thin, not only high efficiency but also favorable reliability of the hermetic refrigerant compressor can be achieved.

In the hermetic refrigerant compressor configured as above, the thrust bearing may include: a lower race positioned on the thrust surface; an upper race positioned facing the lower race; and a plurality of rolling elements that are arranged between the upper and lower races and that are rollably in contact with the upper and lower races. The rolling elements may be balls.

According to the above configuration, even if the thrust bearing is a general ball bearing, increase in the overall height can be avoided, and also, without subjecting the sliding surfaces to special treatment, the load on the main shaft can be reduced and thereby high efficiency can be achieved.

In the hermetic refrigerant compressor configured as above, the lubricating oil may have a kinematic viscosity in a range of 1 mm²/S to 7 mm²/S at 40° C.

According to the above configuration, the lubricating oil has a reduced viscosity. When the distance L is specified within the predetermined range, the distance La is specified to less than or equal to 16 mm. This setting makes it possible to reduce the load on the main shaft without making the flange thin and without subjecting the sliding surfaces to special treatment. Therefore, even though the lubricating oil that is used is low-viscosity oil, reduction of the wear resistance of a slide part formed by the main shaft and the main bearing (i.e., a main shaft slide part) can be effectively suppressed or avoided. Consequently, the efficiency of the hermetic refrigerant compressor can be further heightened without requiring special treatment on the sliding surfaces and without increasing the overall height of the hermetic refrigerant compressor.

In the hermetic refrigerant compressor configured as above, the lubricating oil may have a mass average molecular weight in a range of 150 to 400, and may contain 0.5% by mass or more of a high molecular weight component. The high molecular weight component may have a mass molecular weight of greater than or equal to 500.

According to the above configuration, the average molecular weight of the low-viscosity lubricating oil is within a predetermined range, and the lubricating oil contains the high molecular weight component whose molecular weight is relatively great. Accordingly, even though the lubricating oil is low-viscosity oil, a favorable oil film can be formed by the lubricating oil. This makes it possible to effectively suppress or avoid reduction in the wear resistance of the main shaft slide part. Consequently, the efficiency of the hermetic refrigerant compressor can be further heightened without requiring special treatment on the sliding surfaces and without increasing the overall height of the hermetic refrigerant compressor.

In the hermetic refrigerant compressor configured as above, the lubricating oil may contain an oiliness agent.

According to the above configuration, the low-viscosity lubricating oil contains the oiliness agent in addition to the high molecular weight component. By additionally containing the oiliness agent in the lubricating oil, the formation of the oil film by the lubricating oil can be further facilitated. Consequently, the friction at the main shaft slide part can be reduced more favorably.

In the hermetic refrigerant compressor configured as above, the oiliness agent may be an ester-based compound.

According to the above configuration, since the oiliness agent contained in the lubricating oil is an ester-based compound, the oiliness agent has an ester linkage. Accordingly, owing to the polarity derived from the ester linkage, the oil film formation performance of the oiliness agent can be improved. Consequently, the friction at the main shaft slide part can be reduced more favorably.

In the hermetic refrigerant compressor configured as above, a distillation fraction of the lubricating oil at a distillation temperature of 300° C. may be 0.1% or greater, and a distillation end point may be 440° C. or higher.

According to the above configuration, a component having a high distillation temperature is present in the low-viscosity lubricating oil containing the high molecular weight component. Accordingly, even though the temperature of the slide part increases due to reduction of the sliding area, the evaporation of the lubricating oil can be avoided or suppressed effectively. As a result, the oil film can be more stably formed by the lubricating oil. Consequently, the friction at the main shaft slide part can be reduced more favorably.

In the hermetic refrigerant compressor configured as above, the lubricating oil may contain a sliding modifier such that a content of the sliding modifier in the lubricating oil in terms of an atomic weight of sulfur is greater than or equal to 100 ppm.

According to the above configuration, a suitable amount of the sulfur-based sliding modifier is added to the low-viscosity lubricating oil containing the high molecular weight component. Owing to the sliding modifier, the wear resistance of the sliding surfaces can be improved, which makes it possible to facilitate the reduction of the friction at the main shaft slide part. Accordingly, even in a state where the sliding area is reduced, the friction at the main shaft slide part can be reduced more favorably.

In the hermetic refrigerant compressor configured as above, the lubricating oil may contain a phosphorus-based extreme-pressure additive.

According to the above configuration, the phosphorus-based extreme-pressure additive is added to the low-viscosity lubricating oil containing the high molecular weight component. Owing to the extreme-pressure additive, the wear resistance of the sliding surfaces can be improved, which makes it possible to facilitate the reduction of the friction at the main shaft slide part. Accordingly, even in a state where the sliding area is reduced, the friction at the main shaft slide part can be reduced more favorably.

In the hermetic refrigerant compressor configured as above, the lubricating oil may be at least one selected from the group consisting of mineral oil, alkyl benzene oil, and ester oil.

According to the above configuration, at least one selected from the group consisting of mineral oil, alkyl benzene oil, and ester oil is used as the lubricating oil although the lubricating oil is not particularly limited. As a result, in a case where the lubricating oil is low-viscosity oil containing the high molecular weight component, even in a state where the sliding area is reduced, the frictional coefficient of the main shaft slide part can be readily reduced.

In the hermetic refrigerant compressor configured as above, the electric element may be inverter-driven at a plurality of operating frequencies.

According to the above configuration, in the case where the electric element is inverter-driven, regardless of whether low-speed operation is being performed or high-speed operation is being performed, a favorable oil film is formed at the main shaft slide part by the low-viscosity lubricating oil containing the high molecular weight component. Even in a state where the sliding area is reduced, the frictional coefficient of the shaft part can be reduced favorably. Consequently, the main shaft slide part has a low frictional coefficient and favorable wear resistance regardless of the operating speed. This makes it possible to further improve the efficiency and reliability of the hermetic refrigerant compressor.

In the hermetic refrigerant compressor configured as above, the hermetic refrigerant compressor may be operated at a rotation speed of 35 rps or less.

According to the above configuration, in particular, even during low-speed operation, a low frictional coefficient and favorable wear resistance of the main shaft slide part can be achieved, which makes it possible to further improve the efficiency and reliability of the hermetic refrigerant compressor.

A refrigerator-freezer according to the present disclosure includes a refrigerant circuit including: the hermetic refrigerant compressor configured as above; a radiator; a decompressor; and a heat absorber. In the refrigerant circuit, the hermetic refrigerant compressor, the radiator, the decompressor, and the heat absorber are connected by piping in an annular manner.

The above configuration makes it possible to avoid increase in the overall height of the hermetic refrigerant compressor including the thrust bearing without making the flange thin, and also makes it possible to reduce the load on the main shaft without requiring special treatment on the sliding surfaces. Consequently, high efficiency and favorable reliability of the hermetic refrigerant compressor are achieved. By including the hermetic refrigerant compressor, which is highly efficient and has favorable reliability, in the refrigerator-freezer, the power consumption of the refrigerator-freezer can be reduced, and also, the refrigerator-freezer can be made highly reliable.

Hereinafter, representative embodiments of the present invention are described with reference to the drawings. In the drawings, the same or corresponding elements are denoted by the same reference signs, and repeating the same descriptions is avoided below.

Embodiment 1

[Configuration of Compressor]

First, a representative configuration example of a hermetic refrigerant compressor according to Embodiment 1 of the present disclosure is specifically described with reference to FIG. 1 . FIG. 1 is a schematic sectional view showing one example of the configuration of a hermetic refrigerant compressor 100 according to Embodiment 1 of the present disclosure (hereinafter, basically, the hermetic refrigerant compressor 100 is simply referred to as “refrigerant compressor 100”).

As shown in FIG. 1 , the refrigerant compressor 100 includes a sealed container 102 filled with refrigerant gas 181, which is, for example, R600a. Mineral oil is stored in the bottom of the sealed container 102 as lubricating oil 180. A compressor body 108 is accommodated in the sealed container 102. The compressor body 108 is elastically supported by a suspension spring 190. The compressor body 108 includes an electric element 104 and a compression element 106.

The electric element 104 includes at least a stator 150 and a rotor 152. The compression element 106 is a reciprocating element driven by the electric element 104. The compression element 106 includes, for example, a crankshaft 120, a cylinder block 130, a piston 140, and a coupler 142. The crankshaft 120 includes at least a main shaft 124, an eccentric shaft 122, and a flange 128. The rotor 152 is fixed to the main shaft 124 by shrinkage fitting. The eccentric shaft 122 is formed such that it is eccentric with the main shaft 124. The flange 128 connects between the main shaft 124 and the eccentric shaft 122.

It should be noted that, as shown in FIG. 1 , the eccentric shaft 122 of the crankshaft 120 is positioned in the upper side of the refrigerant compressor 100, whereas the main shaft 124 of the crankshaft 120 is positioned in the lower side of the refrigerant compressor 100. Therefore, this upper-lower positional relationship (direction) is utilized herein when describing positions on the crankshaft 120. For example, the upper end of the eccentric shaft 122 faces the inner upper surface of the sealed container 102, and the lower end of the eccentric shaft 122 is connected to the main shaft 124.

The upper end of the main shaft 124 is connected to the eccentric shaft 122, and the lower end of the main shaft 124 faces the inner lower surface of the sealed container 102. The lower end portion of the main shaft 124 is immersed in the lubricating oil 180. An oil feeding mechanism 125 is provided on the lower part of the crankshaft 120, i.e., on the lower part of the main shaft 124. The oil feeding mechanism 125 feeds the lubricating oil 180 from the lower end of the main shaft 124, which is immersed in the lubricating oil 180, to the upper end of the eccentric shaft 122.

The lubricating oil 180 used in the present disclosure is not particularly limited. In Embodiment 1, as described below, the lubricating oil 180 has a kinematic viscosity in the range of 1 mm²/S to 7 mm²/S at 40° C., has a mass average molecular weight in the range of 150 to 400, and contains 0.5% by mass or more of a high molecular weight component. The high molecular weight component has a mass molecular weight of greater than or equal to 500. It should be noted that, in Embodiment 1, low-viscosity mineral oil is used as a specific example of the lubricating oil 180. However, the lubricating oil 180 is not limited to low-viscosity mineral oil. For example, as described below, an oil substance different from mineral oil may be used as the lubricating oil 180, or the lubricating oil 180 may contain, for example, an oiliness agent or an extreme-pressure additive.

A cylinder 132 and a main bearing 134 are integrally formed on the cylinder block 130. The cylinder 132 forms a compression chamber 133. The main bearing 134 pivotally supports the main shaft 124, such that the main shaft 124 is rotatable. The main bearing 134 has a tubular (cylindrical) shape that extends in the vertical direction relative to the cylinder block 130. The inner peripheral surface of the main bearing 134 is a sliding surface. The main bearing 134 includes a thrust surface 136 and a tubular extension 137.

The thrust surface 136 is a flat surface that spreads in a direction (horizontal direction) orthogonal (perpendicular) to the extending direction (vertical direction) of the main shaft 124, i.e., the center axis. The tubular extension 137 is a tubular (cylindrical) portion that extends further upward from the thrust surface 136. In other words, the tubular extension 137 is a portion that extends upward from the body of the tubular main bearing 134. Accordingly, the tubular extension 137, together with the body of the main bearing 134, includes an inner peripheral surface (sliding surface) that faces the outer peripheral surface (sliding surface) of the main shaft 124. A thrust ball bearing 210 is provided on the thrust surface 136 of the main bearing 134. It should be noted that a specific configuration of the thrust ball bearing 210 will be described below.

The compression chamber 133 is a cylindrical (columnar) bore formed in the cylinder block 130. The piston 140 is inserted in the compression chamber 133 in a reciprocable manner. Therefore, the compression chamber 133 is closed by the piston 140 inserted therein. The coupler 142 is, for example, an aluminum casting product. The coupler 142 pivotally supports the eccentric shaft 122, and is coupled to the piston 140. Thus, the eccentric shaft 122 and the piston 140 are coupled together by the coupler 142.

In the present disclosure, as shown in FIG. 1 , in the cylinder block 130, the compression chamber 133 is positioned above the main bearing 134. Therefore, the center axis of the compression chamber 133 (the center axis of the cylindrical or columnar space (bore)) is positioned above the main bearing 134. In the present disclosure, in a case where a distance in the vertical direction between the center axis of the compression chamber 133 and the lower end of the sliding surface of the main bearing 134 is defined as a distance L, and a distance in the vertical direction between the center axis of the compression chamber 133 and the upper end of the sliding surface of the main bearing 134 is defined as a distance La, when the distance L is in the range of 38 mm to 51 mm, the distance La is less than or equal to 16 mm. It should be noted that each of the distance L and the distance La can be considered as a distance (space) from the center axis of the compression chamber 133 to an end of the sliding surface.

The outer peripheral surface of the main shaft 124 of the crankshaft 120 includes a sliding surface 126 and a non-sliding surface 127. In the present disclosure, the term “sliding surface” means the outer peripheral surface or the inner peripheral surface of each of a plurality of slide members forming a slide part, the outer or inner peripheral surface slidably contacting the other inner or outer peripheral surface. Unlike the sliding surface, the “non-sliding surface” is the outer peripheral surface or the inner peripheral surface that does not come into contact with the other inner or outer peripheral surface. In the present embodiment, the non-sliding surface 127 is formed by reducing (narrowing) the external diameter of a part of the main shaft 124 from the external diameter of the sliding surface 126 (i.e., the non-sliding surface 127 is recessed from the sliding surface 126, or the non-sliding surface 127 is formed by recessing the middle portion of the sliding surface 126).

In the present embodiment, for example, the cylinder block 130 is made of cast iron. The cylinder block 130 forms the substantially cylindrical compression chamber 133, and includes the main bearing 134, which pivotally supports the main shaft 124 of the crankshaft 120. The inner peripheral surface of the main bearing 134 is slidably in contact with the outer peripheral surface, i.e., the sliding surface, of the main shaft 124. Accordingly, the inner peripheral surface of the main bearing 134 also serves as a sliding surface.

In a state where the main shaft 124 is pivotally supported by the main bearing 134, the non-sliding surface 127 of the main shaft 124 is positioned between the upper end and the lower end of the main bearing 134. Therefore, the non-sliding surface 127 is neither exposed from the upper end of the main bearing 134 nor exposed from the lower end of the main bearing 134, and both the upper and lower ends of the main bearing 134 are in contact with the sliding surface 126. It should be noted that the sliding surface 126 of the main shaft 124 may constitute part of the outer peripheral surface of the main shaft 124 as in this example, or may constitute the entire outer peripheral surface of the main shaft 124.

The electric element 104 includes the rotor 152 and the stator 150. The stator 150 is disposed coaxially with the rotor 152 in a manner to surround the rotor 152. The stator 150 is disposed on the outer peripheral side of the rotor 152, such that substantially a constant gap is formed between the stator 150 and the rotor 152. The stator 150 is fixed to the leg of the cylinder block 130. The rotor 152 is fixed to the main shaft 124.

In Embodiment 1, in the sealed container 102, the electric element 104 is positioned in the lower side of the sealed container 102 and the compression element 106 is positioned in the upper side of the sealed container 102. However, the configuration of the refrigerant compressor 100 according to the present disclosure is not thus limited. Alternatively, the electric element 104 may be positioned in the upper side of the sealed container 102, and the compression element 106 may be positioned in the lower side of the sealed container 102. In Embodiment 1, the electric element 104 is an inner rotor type, and the rotor 152 is rotatably disposed on the inner peripheral side of the stator 150, such that the rotor 152 is coaxial with the stator 150. However, the configuration of the electric element 104 is not thus limited. The electric element 104 may be an outer rotor type. That is, the rotor 152 may be rotatably disposed on the outer peripheral side of the stator 150, such that the rotor 152 is coaxial with the stator 150.

In the refrigerant compressor 100 thus configured, first, electric power is supplied from an unshown commercial power supply to the electric element 104 to cause the rotor 152 of the electric element 104 to rotate. The rotor 152 causes the crankshaft 120 to rotate, and eccentric motion of the eccentric shaft 122 is transmitted to the piston 140 via the coupler 142, thereby driving the piston 140 to make reciprocating motion. Due to the reciprocating motion of the piston 140, the refrigerant gas 181 that has been led into the sealed container 102 is sucked into the compression chamber 133, and is compressed therein.

It should be noted that a specific method adopted herein for driving the refrigerant compressor 100 is not particularly limited. For example, the refrigerant compressor 100 may be driven by simple on-off control, or may be inverter-driven at a plurality of operating frequencies. That is, the refrigerant compressor 100 according to Embodiment 1 may include an inverter circuit so as to be able to drive the electric element 104 to rotate at a plurality of operating rotation speeds.

The operating rotation speed of the electric element 104 is not particularly limited. Generally speaking, the operating rotation speed of the electric element 104 is, for example, in the range of 17 to 75 rps (revolutions per second or rotations per second). The upper limit of the operating rotation speed may be 80 rps, and the lower limit of the operating rotation speed may be 13 rps. In the present disclosure, favorable efficiency of the refrigerant compressor 100 can be achieved regardless of whether high-speed operation is being performed or low-speed operation is being performed. In particular, the efficiency of the refrigerant compressor 100 during low-speed operation can be heightened. The rotation speed during low-speed operation is not particularly limited. In the present disclosure, the rotation speed during low-speed operation may be, for example, 35 rps or less as described below.

Among a plurality of slide parts included in the refrigerant compressor 100, the main shaft 124 of the crankshaft 120 is rotatably fitted to the main bearing 134 as described above, and thereby a slide part is formed. Therefore, for the sake of convenience of the description, the slide part thus formed by the main shaft 124 and the main bearing 134 is referred to as a “main shaft slide part”. In accordance with the rotation of the crankshaft 120, an oil-feeding pump feeds the lubricating oil 180 to each slide part, and thereby each slide part is lubricated. It should be noted that the lubricating oil 180 also serves to seal between the piston 140 and the compression chamber 133. In the present disclosure, as described below, low-viscosity oil containing a high molecular weight component can be suitably used as the lubricating oil 180. Such lubricating oil 180 can favorably lubricate each slide part, and also favorably seal between the piston 140 and the compression chamber 133.

[Thrust Bearing and Distances L and La]

Next, with reference to FIG. 1 , FIG. 2 , and FIG. 3 , a specific configuration example of a thrust bearing included in the refrigerant compressor 100 according to Embodiment 1 and one example of the distance L and the distance La, each of which is distance from the center axis of the compression chamber 133 to an end of a sliding surface, are described. Each of FIG. 2 and FIG. 3 schematically shows a partial sectional view of the refrigerant compressor 100 shown in FIG. 1 . FIG. 2 schematically shows one example of the distance L, the distance La, and a load applied to the main shaft slide part (a main shaft load). FIG. 3 schematically shows one configuration example of an essential part of the thrust bearing.

As shown in FIG. 1 , the main bearing 134 has a circular tubular or circular cylindrical shape that extends in the vertical direction relative to the cylinder block 130, which is wide in the horizontal direction in the sealed container 102. The body of the main bearing 134 extends downward from the cylinder block 130. As previously described, since the tubular extension 137 extends upward from the cylinder block 130, the body of the main bearing 134 and the tubular extension 137 form a single circular tubular or circular cylindrical structure.

As previously mentioned, the inner peripheral surface of the main bearing 134 is a sliding surface. Accordingly, as shown in FIG. 2 , the upper edge of the inner peripheral surface of the main bearing 134 is a sliding surface upper end 138, and the lower edge of the main bearing 134 is a sliding surface lower end 139. In Embodiment 1, since the main bearing 134 includes the upper tubular extension 137, the sliding surface upper end 138 corresponds to the upper edge of the inner peripheral surface of the tubular extension 137. In other words, the tubular extension 137 is an “extension portion” that is a result of extending the main bearing 134 upward. Since the main bearing 134 includes the tubular extension 137 thus configured, at the time of defining the upper limit of the distance La, the overall length of the main bearing 134 can be increased without increasing the overall height of the refrigerant compressor 100. This makes it possible to improve the orientation of the crankshaft 120 inserted in the main bearing 134 while the refrigerant compressor 100 is operating.

As shown in FIG. 3 , the upper end inner surface of the tubular extension 137 may be machined, for example, chamfered. In this case, the inner edge of the chamfered portion of the inner surface of the tubular extension 137 is the sliding surface upper end 138 of the main bearing 134. It should be noted that in a case where the upper end inner surface of the tubular extension 137 is not machined, for example, not chambered, the upper edge of the inner surface of the tubular extension 137 is the sliding surface upper end 138 of the main bearing 134.

As shown in FIG. 2 , in a case where the distance between the center axis of the compression chamber 133 and the sliding surface lower end 139 of the main bearing 134 is defined as the “distance L”, and the distance between the center axis of the compression chamber 133 and the sliding surface upper end 138 of the main bearing 134 is defined as the “distance La” as previously described, even though the refrigerant compressor 100 according to the present disclosure includes the thrust bearing such as the thrust ball bearing 210, the distance La is less than or equal to 16 mm when the distance L is in the range of 38 mm to 51 mm.

In the refrigerant compressor 100 according to the present disclosure, the thrust bearing is provided on the thrust surface 136 of the main bearing 134. A specific configuration of the thrust bearing is not particularly limited. Various rolling bearings are adoptable as the thrust bearing. In Embodiment 1, the thrust ball bearing 210 is used as shown in FIG. 1 to FIG. 3 . As shown in FIG. 3 , the thrust ball bearing 210 includes: a lower race 206 positioned on the thrust surface 136; an upper race 202 positioned facing the lower race 206; and balls 204 serving as a plurality of rolling elements that are arranged between the upper and lower races 202 and 206 and that are rollably in contact with the upper and lower races 202 and 206.

The thrust ball bearing 210 is disposed on the outer peripheral side of the tubular extension 137, and the plurality of balls 204 are accommodated in a retainer 205. The upper race 202 and the lower race 206 are, for example, annular metal plates that are arranged parallel to each other. It should be noted that each of the upper race 202 and the lower race 206 may be provided with an arc-shaped groove.

In the configuration example shown in FIG. 3 , the lower race 206, the balls 204, and the upper race 202 are stacked in this order on the thrust surface 136 and are in contact with each other, and the flange 128 of the crankshaft 120 is seated on the upper surface of the upper race 202. The thrust ball bearing 210 is configured in this manner.

The thrust ball bearing 210 is a rolling bearing in which the balls 204 roll while being in point contact with the upper race 202 and the lower race 206. Accordingly, the thrust ball bearing 210 allows the main shaft 124 to rotate with less friction while supporting a load in a perpendicular direction. The thrust ball bearing 210 is a “ball bearing” in which the balls 204 serve as rolling elements. Alternatively, the thrust ball bearing 210 may be a “roller bearing” in which rollers serve as rolling elements, or may be a different type of rolling bearing.

Thus, since the thrust ball bearing 210, which is a rolling bearing, is used instead of a plain bearing, the bearing function is thus changed and thereby a loss is reduced, which makes it possible to effectively heighten the efficiency of the refrigerant compressor 100. However, usually, the installation of the thrust bearing, such as the thrust ball bearing 210, causes increase in the overall height of the refrigerant compressor 100. In this respect, in the refrigerant compressor 100 according to the present disclosure, the distance L and the distance La, each of which is a distance from the center axis of the compression chamber 133, are set such that when the distance L is in the range of 38 mm to 51 mm, the distance La is less than or equal to 16 mm Hereinafter, functions that are obtained by thus setting the upper limit of the distance La are specifically described.

In a case where the refrigerant compressor 100 adopts a one-end support structure of the bearing as in Embodiment 1, a sliding loss W of the main shaft 124 while the refrigerant compressor 100 is operating can be simply calculated by an equation (1) shown below. In the equation (1), F is a load on the main shaft 124; μ is a frictional coefficient between the main shaft 124 and the main bearing 134; and v is a sliding speed of the main shaft 124.

W=F×μ×v  (1)

The load F on the main shaft 124 (main shaft load F) can be calculated by an equation (2) shown below. As shown in FIG. 2 , Fa in the equation (2) is a load from the piston 140 (piston load Fa); La is the distance between the center axis of the compression chamber 133 and the sliding surface upper end 138 as previously described; and L is the distance between the center axis of the compression chamber 133 and the sliding surface lower end 139 as previously described.

F=Fa×{1+La/(L−La)}  (2)

Based on the above equations (1) and (2), in order to heighten the efficiency of the refrigerant compressor 100, i.e., in order to reduce the sliding loss W of the main shaft 124, the frictional coefficient μ may be reduced and/or the main shaft load F may be reduced. Also, in order to reduce the main shaft load F, the distance La may be reduced and/or the distance L may be increased.

However, in order to increase the distance L, it is necessary to increase the overall height of the refrigerant compressor 100. In a case where the overall height is thus increased, the size of an engine room (machinery room) in a refrigerator-freezer in which the refrigerant compressor 100 is installed needs to be increased, which results in reduction in the internal volume of the refrigerator-freezer. In consideration of this, in order to reduce the main shaft load F, it is conceivable to reduce the distance La without changing the distance L.

However, a simple way that can be adopted to reduce the distance La is, for example, as described in Patent Literature 2 as prior art, to reduce the wall thickness of the support portion of the cylinder block 130, or as described in Patent Literature 3, to reduce the thickness of the flange 128 to 4 mm or less. That is, it is conceivable to adopt a technique to reduce the wall thickness of a particular component (or a part of the particular component) (wall thickness reduction technique).

However, if such a wall thickness reduction technique is adopted, it consequently causes deformation of other components. Specifically, in a case where the wall thickness of the support portion of the cylinder block 130 is reduced, the stiffness of the cylinder block 130 is reduced, accordingly. As a result, deformation of the main bearing 134 tends to occur. In a case where the wall thickness of the flange 128 is reduced, the inclination of the eccentric shaft 122 increases. In particular, the conventional art does not take into consideration at all such increase in the inclination of the eccentric shaft 122 due to the reduction of the wall thickness of the flange 128. By thus reducing the distance La with the wall thickness reduction technique, the efficiency of the refrigerant compressor 100 can be heightened. In this case, however, there is a risk that the reliability of the refrigerant compressor 100 may be reduced due to deformation of a particular component.

Patent Literature 2 avoids the use of the wall thickness reduction technique by adopting a configuration in which the overall height of the sealed container 102 is set to 6 times or less as large as the diameter of the piston 140 and the half or more of the overall length of the main bearing 134 is accommodated in the hole of the rotor 152, or by adopting a configuration in which the lower end of the main bearing 134 extends downward from the stator 150 in a case where the electric element 104 is an outer rotor type.

In light of the above, the inventors of the present invention have conducted diligent studies, and as a result of the studies, they have found on their own that, as indicated by results of Example 1 described below, by setting the upper limit of the distance La to a predetermined value, specifically to a value less than or equal to 16 mm, both high efficiency and favorable reliability can be achieved without adopting the wall thickness reduction technique (see FIG. 5 ).

Specifically, according to the above equations (1) and (2), in the attempt to reduce the sliding loss W of the main shaft 124, the idea of reducing the distance La can be seen as a way to reduce the main shaft load F. However, the conventional art does not take into consideration the problem in that the reliability of the refrigerant compressor 100 is reduced as a result of reducing the distance La.

However, the inventors of the present invention have found on their own that in a case where the distance La is reduced, a slight inclination (inclination angle) of the eccentric shaft 122, the slight inclination occurring while the refrigerant compressor 100 is operating, affects not only the reliability of the refrigerant compressor 100 but also heightening of the efficiency of the refrigerant compressor 100. In other words, the inventors of the present invention have found on their own that a change in the distance La and an inclination of the eccentric shaft 122 are important factors for reducing the main shaft load F to achieve high efficiency and favorable reliability of the refrigerant compressor 100. Consequently, the inventors of the present invention have also found on their own that it is important to set the upper limit of the distance La to less than or equal to 16 mm.

In the present disclosure, the distance L and the distance La are set such that when the distance L is in the range of 38 mm to 51 mm, the distance La is less than or equal to 16 mm A preferable range of the distance La is set to 12 mm to 16 mm (i.e., the lower limit value of the distance La is, as one example, 12 mm). Therefore, it is not necessary to increase the overall height of the refrigerant compressor 100. This makes it possible not only to achieve high efficiency of the refrigerant compressor 100 while maintaining favorable quality (in particular, favorable reliability) of the refrigerant compressor 100, but also to eliminate the necessity to increase the size of the engine room (machinery room) of the refrigerator-freezer. Consequently, a sufficient internal volume of the refrigerator-freezer can be secured.

In Patent Literature 2, the overall height of the sealed container 102 is defined with reference to the diameter of the piston 140. On the other hand, in the present disclosure, it is not particularly necessary to limit the diameter of the piston 140 or the internal diameter of the compression chamber 133 in which the piston 140 is inserted. In the refrigerant compressor 100 according to the present disclosure, the internal diameter (bore diameter) of the compression chamber 133 (bore) is not particularly limited. In the present embodiment, the internal diameter (bore diameter) of the compression chamber 133 (bore) may be in the range of 22 mm to 28 mm. Setting the distance La such that the distance La is less than or equal to 16 mm when the distance L is in the range of 38 mm to 51 mm makes it possible not only to eliminate the necessity to make the flange 128 excessively thin, but also to keep the internal diameter of the compression chamber 133 within the aforementioned range.

Based on the above equations (1) and (2), other than reducing the distance La, it is conceivable to reduce the frictional coefficient μ between the main shaft 124 and the main bearing 134 in order to reduce the sliding loss W. A simple conceivable way to reduce the frictional coefficient μ is, as described in Patent Literature 1, to use low-viscosity lubricating oil 180. However, in a case where the lubricating oil 180 has a low viscosity, it is difficult to form, with the lubricating oil 180, a sufficient oil film for lubrication. If a sufficient oil film for lubrication is not formed, there is a risk of wear or seizing of the main shaft 124 and the main bearing 134. For this reason, in Patent Literature 1, the sliding surfaces are subjected to special treatment.

In light of the above, the inventors of the present invention have conducted diligent studies, and as a result of the studies, they have found on their own that, as indicated by results of Examples 2 to 4 described below, by not only setting the distance La to less than or equal to 16 mm (i.e., reducing the main shaft load F), but also using the low-viscosity lubricating oil 180 containing a high molecular weight component, both efficiency and reliability of the refrigerant compressor 100 can be further improved (see FIG. 6 and FIG. 7 ).

Specifically, in the case of adopting a technique of simply using low-viscosity lubricating oil 180, wear or seizing of the main shaft 124 and the main bearing 134 cannot be effectively prevented or suppressed, and for this reason, it has been thought that using low-viscosity oil as the lubricating oil 180 is not suitable for securing the quality of the refrigerant compressor 100.

However, the inventors of the present invention have found on their own that since the main shaft load F can be reduced by setting the distance La of the refrigerant compressor 100 to less than or equal to 16 mm as described above, the frictional coefficient μ between the main shaft 124 and the main bearing 134 can be relatively reduced, accordingly, and for this reason, relatively low-viscosity oil can be used as the lubricating oil 180. Further, it has also been found that by using low-viscosity oil containing a high molecular weight component as the lubricating oil 180, a more favorable oil film can be formed, which makes it possible to further enhance the functional advantage of achieving both high efficiency and favorable reliability.

In particular, while the refrigerant compressor 100 is performing low-speed operation, the sliding environment for the main shaft slide part is severe, and if the lubricating oil 180 is low-viscosity oil, a favorable oil film is not easily formed by the lubricating oil 180. In this respect, according to the present disclosure, the main shaft load F is reduced by setting the distance La to less than or equal to 16 mm. Therefore, even though the lubricating oil 180 is low-viscosity oil, a favorable oil film is easily formed by the lubricating oil 180 during low-speed operation. This makes it possible to effectively suppress or avoid wear or seizing of the main shaft 124 and the main bearing 134.

It should be noted that the upper limit of the operating rotation speed of the refrigerant compressor 100 during low-speed operation is not particularly limited, but may be suitably set in accordance with a specific operating rotation speed range that is based on the operating performance of the refrigerant compressor 100. For example, a rotation speed less than a median value within the specific operating rotation speed range can be defined as a relatively low operating rotation speed.

In the present disclosure, as previously described, one example of a general operating rotation speed is in the range of 17 to 75 rps. In this case, as indicated by results of Example 3, Example 4, and Comparative Example described below, even when the operating rotation speed is 35 rps or less, by setting the distance La to less than or equal to 16 mm, the efficiency (coefficient of performance) of the refrigerant compressor 100 can be improved significantly. Therefore, in the present disclosure, low-speed operation can be defined as operation at an operating rotation speed of 35 rps or less.

Further, from the comparison of the results of Example 3, Example 4, and Comparative Example, it is understood that as compared to the degree of improvement in the coefficient of performance of each of Examples 3 and 4 from Comparative Example at an operating rotation speed of 35 rps, the degree of improvement in the coefficient of performance of each of Examples 3 and 4 from Comparative Example is the same degree or higher when the operating rotation speed is lowered to 30 rps, 25 rps, 20 rps, and 17 rps. Therefore, in the present disclosure, the upper limit of the operating rotation speed during low-speed rotation can be suitably set based on the results of Example 3 and Example 4 (see FIG. 7 ). Thus, in the present disclosure, in particular, even during low-speed operation, a low frictional coefficient and favorable wear resistance of the main shaft slide part can be achieved, which makes it possible to further improve the efficiency and reliability of the hermetic refrigerant compressor 100.

In the present embodiment, as shown in FIG. 1 and FIG. 2 , the eccentric shaft 122 is provided on the upper part (upper end) of the main shaft 124; the piston 140 is coupled to the eccentric shaft 122 via the coupler 142; and the piston 140 is inserted in the compression chamber 133, which is disposed horizontally, such that the piston 140 is reciprocable. That is, in the present embodiment, the piston 140 and the compression chamber 133 are positioned in the upper part of the refrigerant compressor 100. However, the configuration of the refrigerant compressor 100 according to the present disclosure is not thus limited.

For example, although not illustrated, by providing the eccentric shaft 122 on the lower part (lower end) of the main shaft 124, the piston 140 and the compression chamber 133 may be positioned in the lower part of the refrigerant compressor 100. In this case, the distance L is defined as a distance between the center axis of the compression chamber 133 and the sliding surface upper end, and the distance La is defined as a distance between the center axis of the compression chamber 133 and the sliding surface lower end.

In the present embodiment, as shown in FIG. 1 , the crankshaft 120 extends in the vertical direction (longitudinal direction) of the refrigerant compressor 100. Accordingly, the main shaft 124 and the eccentric shaft 122 also extend in the vertical direction. However, the configuration of the refrigerant compressor 100 according to the present disclosure is not thus limited. For example, the crankshaft 120 may extend in the horizontal direction (lateral direction), and the piston 140 and the compression chamber 133 may be not positioned in the upper or lower part of the refrigerant compressor 100, but positioned locally on one side in the horizontal direction in the refrigerant compressor 100. In this case, both of the sliding surface ends, which serve as the references for the respective distances L and La, are positioned not in the vertical direction, but in the horizontal direction.

Accordingly, in the present disclosure, one end of the sliding surface of the main bearing 134, the one end being closer to the compression chamber 133 (or the eccentric shaft 122) than an opposite end of the sliding surface is defined as a first end, and the opposite end of the sliding surface is defined as a second end. Therefore, the distance L can be defined as a distance between the center axis of the compression chamber 133 and the second end of the sliding surface of the main bearing 134, whereas the distance La can be defined as a distance between the center axis of the compression chamber 133 and the first end of the sliding surface of the main bearing 134. In the present embodiment (the example shown in FIG. 1 or FIG. 2 ), the sliding surface upper end 138 is the first end, and the sliding surface lower end 139 is the second end.

It should be noted that, in the present disclosure, the crankshaft 120 (the main shaft 124 and the eccentric shaft 122) can be defined, for example, as extending in a first direction. In the present embodiment (the example shown in FIG. 1 or FIG. 2 ), the vertical direction is the first direction, and the horizontal direction is a second direction. Accordingly, the direction of the reciprocating motion of the piston 140 is the second direction, and also, the direction in which the compression chamber 133 is disposed (i.e., the direction of the center axis of the compression chamber 133) is the second direction. In a case where the crankshaft 120 extends in the horizontal direction, the horizontal direction is the first direction, and the vertical direction is the second direction.

[Configuration of Lubricating Oil]

Next, low-viscosity lubricating oil that contains a high molecular weight component and that is particularly preferably used as the lubricating oil 180 in the refrigerant compressor 100 according to the present disclosure is specifically described. It should be noted that, in the present disclosure, the lubricating oil 180 is not limited to low-viscosity oil containing a high molecular weight component. Therefore, in the description below, low-viscosity lubricating oil containing a high molecular weight component is referred to as “suitable lubricating oil” for the sake of convenience of the description.

In the present embodiment, the suitable lubricating oil used as the lubricating oil 180 is low-viscosity oil that has a kinematic viscosity in the range of 1 mm²/S to 7 mm²/S at 40° C., has a mass average molecular weight in the range of 150 to 400, and contains 0.5% by mass or more of a high molecular weight component. The high molecular weight component has a relatively high molecular weight, i.e., has a mass molecular weight of greater than or equal to 500. A specific material of the suitable lubricating oil is not particularly limited. Typically, for example, at least one oil substance selected from the group consisting of mineral oil, alkyl benzene oil, and polyalkylene glycol oil can be suitably used as the suitable lubricating oil.

The suitable lubricating oil used in the present embodiment may originally contain the high molecular weight component. Alternatively, an oil substance serving as the high molecular weight component may be added to the suitable lubricating oil, such that the suitable lubricating oil contains 0.5% by mass or more of the high molecular weight component. In the former case, for example, mineral oil may be used as the suitable lubricating oil. Unrefined or roughly refined raw material mineral oil may be refined to prepare (produce) the suitable lubricating oil. At the time, refining conditions or refining technique for refining the raw material oil may be adjusted such that 0.5% by mass or more of the high molecular weight component remains after the refining. In the latter case, for example, mineral oil, alkyl benzene oil, or polyalkylene glycol oil may be contained in the suitable lubricating oil as its “principal component” and an oil substance serving as the high molecular weight component may be added as an “additive component” to the principal component.

As previously mentioned, the mass average molecular weight of the suitable lubricating oil used in the present embodiment may be in the range of 150 to 400. In a case where the mass average molecular weight of the suitable lubricating oil is within this range, the aforementioned kinematic viscosity range at 40° C. is achieved favorably, and also in this case, by containing 0.5% by mass or more of the high molecular weight component in the suitable lubricating oil and setting the distance La to less than or equal to 16 mm, a favorable oil film can be formed on the main shaft slide part (i.e., the slide part between the main shaft 124 and the main bearing 134). The mass average molecular weight of the suitable lubricating oil may be in the range of 200 to 300. If the mass average molecular weight of the suitable lubricating oil is within this range, although depending on various conditions, a favorable oil film can be formed more easily on the main shaft slide part when the distance La is set to less than or equal to 16 mm.

In a case where the suitable lubricating oil is prepared by adding the high molecular weight component to the principal component, a specific material or specific kind of the high molecular weight component is not particularly limited. The high molecular weight component may be an oil substance whose mass molecular weight is greater than or equal to 500. For example, in a case where the principal component is mineral oil, the high molecular weight component may also be mineral oil, or the high molecular weight component may be alkyl benzene oil, polyalkylene glycol oil, or a different oil substance.

A method of measuring the mass average molecular weight of the suitable lubricating oil and the mass molecular weight of the high molecular weight component is not particularly limited. In the present disclosure, these weights can be measured and expressed in terms of standard polystyrene by GPC (Gel Permeation Chromatography) technique that is used in Example 2 described below. That is, the mass average molecular weight (weight average molecular weight) of the suitable lubricating oil may be measured by GPC technique as a weight (mass) average molecular weight in terms of polystyrene. To determine whether or not the mass molecular weight of the high molecular weight component is greater than or equal to 500, a molecular weight distribution graph indicating a relationship between differential molar mass distribution and mass molecular weight may be measured by GPC technique. By using the molecular weight distribution graph, whether or not the mass molecular weight of the high molecular weight component is greater than or equal to 500 may be determined based on whether or not the mass molecular weight has a peak greater than or equal to 500.

In the suitable lubricating oil used in the present embodiment, the lower limit content of the high molecular weight component may be 0.5% by mass, and the upper limit content of the high molecular weight component is not particularly limited, so long as the upper limit content does not affect, at least, the functions of the suitable lubricating oil or the functional advantages provided by the suitable lubricating oil. According to Example 2 described below (see FIG. 6B), in a case where the suitable lubricating oil contains at least 0.5% by mass of the high molecular weight component, the coefficient of performance (COP) of the refrigerant compressor 100 is improved as compared to a case where the suitable lubricating oil does not contain the high molecular weight component (0% by mass).

Further, according to the Example 2 described below (see FIG. 6B), one preferable example of the upper limit content of the high molecular weight component in the suitable lubricating oil is less than or equal to 7.0% by mass. The upper limit content of the high molecular weight component is more preferably less than or equal to 6.0% by mass, and yet more preferably 5.0% by mass. As compared to a case where the suitable lubricating oil does not contain the high molecular weight component (0% by mass), the coefficient of performance is improved even in a case where the content of the high molecular weight component in the suitable lubricating oil is greater than 7.0% by mass. However, in a case where the content of the high molecular weight component in the suitable lubricating oil is greater than 7.0% by mass, it is possible that the coefficient of performance improving effect obtained in this case is unfavorably disproportionate to the content of the high molecular weight component. In light of this, in the present embodiment, the upper limit content of the high molecular weight component may be set to less than or equal to 7.0% by mass.

Still further, according to the Examples described below, in a case where the content of the high molecular weight component is less than or equal to 6.0% by mass, the coefficient of performance is better than in a case where the content of the high molecular weight component is greater than 6.0% by mass. In light of this, in the present embodiment, a preferable upper limit content of the high molecular weight component is less than or equal to 6.0% by mass. Still further, according to the Examples described below, in a case where the content of the high molecular weight component is about 2.0 to 2.5% by mass, the coefficient of performance exhibits its maximal value. Even in a case where the suitable lubricating oil contains about 5.0% by mass of the high molecular weight component, the coefficient of performance is similar to that in a case where the suitable lubricating oil contains 0.5% by mass of the high molecular weight component, which is the lower limit content of the high molecular weight component. In light of this, in the present embodiment, a more preferable upper limit content of the high molecular weight component is less than or equal to 5.0% by mass.

Accordingly, in the present embodiment, the content of the high molecular weight component in the suitable lubricating oil is preferably in the range of 0.5% by mass to 7.0% by mass, more preferably in the range of 0.5% by mass to 6.0% by mass, and yet more preferably in the range of 0.5% by mass to 5.0% by mass. It should be noted that, depending on various conditions of the refrigerant compressor 100 or various conditions of a shaft part to be lubricated, it is possible that the maximal value of the coefficient of performance is shifted to the high molecular weight component content decreasing side or to the high molecular weight component content increasing side. In such a case, the upper limit content of the high molecular weight component may be set to a value greater than 7.0% by mass, or to a value less than 0.5% by mass.

It should be noted that if the content of the high molecular weight component in the suitable lubricating oil is within any of the aforementioned preferable ranges, it is basically determined that the mass average molecular weight of the suitable lubricating oil is in the range of 150 to 400. Specifically, if the ratio of the high molecular weight component to the suitable lubricating oil is within any of the aforementioned preferable ranges, it can be assumed that, when looking at the suitable lubricating oil as a whole, the high molecular weight component barely affects increase in the mass average molecular weight (i.e., the mass average molecular weight of the suitable lubricating oil does not exceed 400). Thus, the upper limit content of the high molecular weight component in the suitable lubricating oil can be set within such a range as not to affect the functions of the suitable lubricating oil and not to cause excessive increase in the mass average molecular weight.

In the present embodiment, the reason why the coefficient of performance of the refrigerant compressor 100 is improved by containing the high molecular weight component in the suitable lubricating oil is, as the results in the below-described Examples 2 and 4 indicate (see FIG. 6B and FIG. 7 ), that even though the suitable lubricating oil has a low viscosity (the kinematic viscosity at 40° C. is in the range of 1 mm²/S to 7 mm²/S), the suitable lubricating oil contributes to the formation of a favorable oil film at the slide part owing to the high molecular weight component. Specifically, while the main shaft 124 supported by the main bearing 134 is sliding, the high molecular weight component can be present on the outer peripheral surface (sliding surface) of the main shaft 124 and the inner peripheral surface (sliding surface) of the main bearing 134, the outer and inner peripheral surfaces forming the main shaft slide part, regardless of the entire flow of the suitable lubricating oil at the main shaft slide part, and thereby the oil film is favorably formed by the suitable lubricating oil.

In the present embodiment, only one oil substance may be used as the suitable lubricating oil, or a suitable combination of two or more oil substances may be used as the suitable lubricating oil. The definition of a combination of two or more oil substances herein includes not only a combination of, for example, two or more different oil substances, each of which is mineral oil, but also a combination of, for example, at least one oil substance that is mineral oil and at least one oil substance that is alkyl benzene oil (or at least one oil substance that is polyalkylene glycol oil).

In a case where the suitable lubricating oil is prepared by adding the high molecular weight component as an additive component to the principal component, for example, one oil substance may be used as the principal component, and another oil substance different from the principal component may be used as the high molecular weight component. Alternatively, two or more oil substances may be used as the principal component, and one oil substance may be used as the high molecular weight component. Further alternatively, one oil substance may be used as the principal component, and two or more oil substances may be used as the high molecular weight component. Still further alternatively, two or more different oil substance mixtures, in each of which the high molecular weight component is added to the principal component, may be mixed together to prepare the suitable lubricating oil.

The oil substances used in the present embodiment are not particularly limited. At least one oil substance from among mineral oil, alkyl benzene oil, and ester oil may be used as the principal component and/or the high molecular weight component. The suitable lubricating oil thus prepared makes it possible to favorably achieve, even in a state where the sliding area is reduced, the effect of reducing the frictional coefficient of the shaft part.

The physical properties of the suitable lubricating oil (oil substance or lubricating oil composition) used in the present embodiment are not particularly limited except the aforementioned kinematic viscosity at 40° C. Preferable physical properties of the suitable lubricating oil are, for example, such distillation properties that the distillation fraction of the suitable lubricating oil at a distillation temperature of 300° C. is 0.1% or greater and the distillation end point is 440° C. or higher. A method of measuring the distillation properties is not particularly limited. In the present embodiment, a measurement method in compliance with JIS K2254: 1998 “Petroleum products-Determination of distillation characteristics” or in compliance with JIS K2601: 1998 “Testing methods for crude petroleum” is used.

At the slide part formed by the shaft part and bearing part, heat is generated due to friction between sliding surfaces upon sliding motion, and it is known that at an early stage of the friction, an instantaneous temperature rise called “flash temperature” occurs. The outer peripheral surface of the shaft part and the inner peripheral surface of the bearing part are configured as smooth sliding surfaces so as to achieve favorable slidability. However, even though the sliding surfaces are macroscopically smooth surfaces, there are microscopically fine protrusions on the sliding surfaces. During sliding motion, the fine protrusions of one sliding surface repeatedly adhere to and break away from the other sliding surface. When the fine protrusions of the one sliding surface break away from the other sliding surface, thermal energy is released, and when the released thermal energy concentrates, an instantaneous temperature rise occurs. A high temperature resulting from the instantaneous temperature rise is hereinafter called “flash temperature”.

For example, Reference Literature 1: Japanese Laid-Open Patent Application Publication No. 2006-097096 discloses a carburized or carbonitrided bearing steel component. According to Reference Literature 1, generally speaking, seizing occurs when the flash temperature exceeds about 140° C. It is also known that the flash temperature at the slide part reaches several hundred degrees Celsius. In the present embodiment, in the case of using the suitable lubricating oil, which is low-viscosity oil containing the high molecular weight component, a condition that the flash temperature at the slide part is 300° C. or higher is important.

Therefore, preferably, the distillation properties of the suitable lubricating oil (oil substance or lubricating oil composition) used in the present embodiment are such that the distillation fraction (volume fraction) of the suitable lubricating oil at a distillation temperature of 300° C. is 0.1% or greater and the distillation end point is 440° C. or higher. In a case where the suitable lubricating oil has these preferable distillation properties, even when the flash temperature of 300° C. or higher occurs at the slide part, problems such as the evaporation of the oil film formed by the suitable lubricating oil can be suppressed or prevented effectively. Consequently, even though the suitable lubricating oil is low-viscosity oil containing the high molecular weight component and the temperature of the slide part increases due to the reduction of the sliding area, the oil film can be more stably formed by the suitable lubricating oil.

The suitable lubricating oil used in the present embodiment may be a low-viscosity oil substance containing the high molecular weight component. Various additives may be added to the oil substance. In other words, the suitable lubricating oil used in the present embodiment may be a lubricating oil composition that contains not only the oil substance but also another component. As previously described, only one oil substance may be used as the suitable lubricating oil, or a combination of two or more oil substances may be used as the suitable lubricating oil. Also in the case of using a combination of two or more oil substances as the suitable lubricating oil, the suitable lubricating oil may be defined as a “lubricating oil composition”. Alternatively, in the case of using a combination of two or more oil substances as the suitable lubricating oil, the suitable lubricating oil may be defined as “mixed oil”, whereas in the case of containing not only the oil substance but also another component in the suitable lubricating oil, the suitable lubricating oil may be defined as a “lubricating oil composition”.

In a case where the suitable lubricating oil used in the present embodiment is a lubricating oil composition that contains not only the oil substance but also another component, this other component is not particularly limited to a specific component. A typical example of the other component is an additive known in the field of general lubricating oil. In particular, in the present embodiment, the suitable lubricating oil preferably contains an oiliness agent. By adding the oiliness agent to the suitable lubricating oil, the formation of the oil film on the sliding surfaces of the slide part by the suitable lubricating oil is facilitated. Consequently, the friction at the slide part can be reduced more favorably.

The oiliness agent is not particularly limited to a specific kind of oiliness agent. Typical examples of the oiliness agent include higher fatty acids, higher alcohols, esters (ester-based compounds), ethers, amines, amides, and metal soaps. Only one of these oiliness agents may be used, or two or more of these oiliness agents may be suitably used in combination. The addition amount(s) of the oiliness agent(s) is/are not particularly limited, and the oiliness agent(s) may be added in the range of, for example, 0.01 to 1% by weight.

In the present embodiment, a more preferable example of the oiliness agent is an ester-based compound. The ester-based compound may be a compound having an ester structure in which an alcohol and a carboxylic acid are reacted with each other. The alcohol may be a monohydric alcohol, or may be a polyhydric alcohol, which is at least bivalent. Similarly, the carboxylic acid may be a monocarboxylic acid, a dicarboxylic acid, or a tricarboxylic acid (or may be a carboxylic acid containing four or more carboxyl groups). Generally speaking, a commercially available ester-based oiliness agent can be suitably used.

As previously described, the suitable lubricating oil used in the present embodiment is low-viscosity oil containing the high molecular weight component. In a case where the suitable lubricating oil is a lubricating oil composition containing the oiliness agent, the oil film formation performance can be further improved. As previously described, since the suitable lubricating oil used in the present embodiment contains the high molecular weight component, the high molecular weight component is present on the sliding surfaces of the main shaft 124 and the main bearing 134, the sliding surfaces forming a slide part, and consequently, the oil film can be favorably formed by the suitable lubricating oil. Further, by containing the oiliness agent in the suitable lubricating oil, the oiliness agent adheres to the sliding surfaces of the main shaft 124 and the main bearing 134, and thereby the formation of the oil film by the suitable lubricating oil (lubricating oil composition) is further facilitated.

In particular, in a case where the oiliness agent is an ester-based compound, the oiliness agent has an ester linkage. Accordingly, owing to the polarity derived from the ester linkage, the adhesion of the oil film formed by the suitable lubricating oil (lubricating oil composition) to the slide part can be further facilitated (i.e., the adhesiveness of the oil film can be further improved), which makes it possible to further improve the oil film formation performance of the suitable lubricating oil. Therefore, the frictional coefficient can be further reduced, and the friction at the slide part can be reduced more favorably.

The suitable lubricating oil used in the present embodiment may contain, as additives, not only the above-described oiliness agent but also a sulfur-based sliding modifier. The sulfur-based sliding modifier may be a sulfur-based sliding modifier that allows the material of the shaft part such as the main shaft 124 (i.e., shaft part material) and sulfur to react with each other. Accordingly, the sliding modifier may be sulfur, or may be a sulfur compound that contains sulfur and that is reactive with the shaft part material.

In the present embodiment, since the material of the shaft part is a ferrous material, examples of sulfur compounds usable as the sliding modifier include sulfurized olefins, sulfide-based compounds (e.g., dibenzyl disulfide (DBDS)), xanthates, thiadiazoles, thiocarbonates, sulfurized oil or fat, sulfurized esters, dithiocarbamates, and sulfurized terpenes.

The content of the sulfur-based sliding modifier in the suitable lubricating oil is not particularly limited. Preferably, the sliding modifier may be added to the suitable lubricating oil, such that the content of the sliding modifier in the suitable lubricating oil in terms of the atomic weight of sulfur is greater than or equal to 100 ppm. It should be noted that the upper limit addition amount of the sliding modifier is not particularly limited, so long as the upper limit addition amount is such an amount (e.g., 1000 ppm or less) as not to affect the physical properties of the suitable lubricating oil (lubricating oil composition).

As previously described, the suitable lubricating oil used in the present embodiment is low-viscosity oil containing the high molecular weight component. In a case where the suitable lubricating oil is a lubricating oil composition containing the sliding modifier in addition to the oiliness agent, the wear resistance of the sliding surfaces can be improved by the sliding modifier. Accordingly, even in a state where the sliding area is reduced, the friction at the slide part can be reduced more favorably.

The suitable lubricating oil used in the present embodiment may contain, as additives, not only the above-described oiliness agent and sliding modifier but also a known extreme-pressure additive. A specific extreme-pressure additive to be added to the suitable lubricating oil is not particularly limited, and a known extreme-pressure additive can be suitably used. Examples of known extreme-pressure additives that can be suitably used include phosphorus-based compounds, such as phosphate esters, and halogenated compounds, such as chlorine-based hydrocarbons or fluorine-based hydrocarbons. Only one of these extreme-pressure additives may be added to the lubricating oil composition (suitable lubricating oil), or a suitable combination of two or more of these extreme-pressure additives may be added to the lubricating oil composition (suitable lubricating oil).

Among these extreme-pressure additives, a phosphorus-based compound can be used preferably. Typical examples of the phosphorus-based compound include tricresyl phosphate (TCP), tributyl phosphate (TBP), and triphenyl phosphate (TPP). Among these, TCP is particularly preferable. In addition to the sulfur-based sliding modifier, a phosphorus-based extreme-pressure additive may be added to the suitable lubricating oil, and thereby, for example, wear of the main shaft slide part can be reduced favorably.

The amount of the extreme-pressure additive to be added to the lubricating oil composition is not particularly limited. For example, in a case where the principal component of the suitable lubricating oil is a low-polarity substance such as mineral oil or alkyl benzene oil, a suitable addition amount of the extreme-pressure additive is in the range of 0.5 to 8.0% by weight, and more preferably in the range of 1 to 3% by weight.

As previously described, the suitable lubricating oil used in the present embodiment is low-viscosity oil containing the high molecular weight component. In a case where the suitable lubricating oil is a lubricating oil composition containing the extreme-pressure additive in addition to the oiliness agent, the wear resistance of the sliding surfaces can be improved by the extreme-pressure additive. In particular, by containing both the sliding modifier and the extreme-pressure additive in the suitable lubricating oil, wear of the sliding surfaces can be reduced more favorably by their synergistic effect. Accordingly, even in a state where the sliding area is reduced, the friction at the slide part can be reduced more favorably.

Further, in the present embodiment, known various additives may be added to the suitable lubricating oil in addition to the oiliness agent, the sliding modifier, and the extreme-pressure additive. Those known in the field of general lubricating oil can be suitably used as the various additives to be added to the suitable lubricating oil. Typical examples of such additives include antioxidants, acid-acceptors, metal deactivators, defoaming agents, anti-corrosive agents, and dispersants.

In other words, the suitable lubricating oil used in the refrigerant compressor 100 according to the present embodiment may be a low-viscosity oil substance containing a high molecular weight component (the low-viscosity oil substance may be formed by only one oil substance, or may be mixed oil containing two or more oil substances). Preferably, the suitable lubricating oil may be a lubricating oil composition (formed by an oil substance and an oiliness agent) that is prepared by adding the oiliness agent to the oil substance. As another preferable example, the lubricating oil composition may contain, as the additive(s), a sliding modifier and/or an extreme-pressure additive.

As described above, in the refrigerant compressor 100 according to the present disclosure, the compression element 106 extends in the vertical direction, and includes the crankshaft 120 including the main shaft 124 and the eccentric shaft 122. The main shaft 124 is pivotally supported by the main bearing 134. The thrust bearing (e.g., the thrust ball bearing 210) is provided on the thrust surface 136 of the main bearing 134. In a case where the distance between the center axis of the compression chamber 133 and the sliding surface lower end 139 of the main bearing 134 is defined as the distance L, and the distance between the center axis of the compression chamber 133 and the sliding surface upper end 138 of the main bearing 134 is defined as the distance La, when the distance L is in the range of 38 mm to 51 mm, the distance La is less than or equal to 16 mm.

According to the above configuration, in the hermetic refrigerant compressor including the thrust bearing, when the distance L, which affects the overall height of the hermetic refrigerant compressor, is specified within a predetermined range, the upper limit of the distance La between the center axis of the compression chamber 133 and the sliding surface upper end 138 of the main bearing 134 is specified to 16 mm. This makes it possible to avoid increase in the overall height of the hermetic refrigerant compressor without making the flange 128 excessively thin, the flange 128 contributing to the stability of the eccentric shaft 122, and also makes it possible to reduce the load on the main shaft 124 without subjecting the sliding surfaces to special treatment. Consequently, the efficiency of the hermetic refrigerant compressor can be further heightened without increasing the overall height of the hermetic refrigerant compressor. In addition, since the flange 128 is not made excessively thin, not only high efficiency but also favorable reliability of the hermetic refrigerant compressor can be achieved.

Embodiment 2

In Embodiment 2, one example of a refrigerator-freezer that includes the refrigerant compressor 100 described above in Embodiment 1 is specifically described with reference to FIG. 4 .

The refrigerant compressor 100 according to the present disclosure can be widely and suitably used in various apparatuses (refrigerator-freezers) that include a refrigeration cycle or that include substantially the same elements as those of the refrigeration cycle. Specific examples of such apparatuses include refrigerators (household refrigerators, professional-use refrigerators), ice-making machines, showcases, dehumidifiers, heat-pump-type water heaters, heat-pump-type washing and drying machines, vending machines, air conditioners, and air compressors. These are non-limiting examples. In Embodiment 2, a fundamental configuration of the refrigerator-freezer is described by taking a product storage apparatus shown in FIG. 4 as one example of application of the refrigerant compressor 100 according to the present disclosure.

As shown in FIG. 4 , the refrigerator-freezer according to Embodiment 4 includes, for example, a body 301, a dividing wall 304, and a refrigerant circuit 305. The body 301 is constituted by a thermally-insulated box, a door, and so forth. The box is configured to have one opening face, and the door is configured to open/close the opening of the box. The interior of the body 301 is divided by the dividing wall 304 into a product storage space 302 and a machinery room 303. An unshown air feeder is provided in the storage space 302. It should be noted that the interior of the body 301 may be divided into, for example, spaces that are different from the storage space 302 and the machinery room 303.

The refrigerant circuit 305 is configured to cool the inside of the storage space 302. The refrigerant circuit 305 includes the refrigerant compressor 100 described above in Embodiment 1, a radiator 307, a decompressor 308, and a heat absorber 309, which are connected by piping in an annular manner. That is, the refrigerant circuit 305 is one example of a refrigeration cycle using the refrigerant compressor 100 according to the present disclosure.

As previously described, the inside of the refrigerant compressor 100 (i.e., the inside of the sealed container 102) is filled with the refrigerant gas 181, which is, for example, R600a. The refrigerant gas 181 filling the inside of the refrigerant compressor 100 is in a relatively low-temperature state such that the pressure of the refrigerant gas 181 is substantially equal to the pressure in the low-pressure side of the refrigerator-freezer. The refrigerant gas 181 is not particularly limited to a specific kind of refrigerant gas. Hydrocarbon-based refrigerant gas having a low global warming potential, such as R600a, can be suitably used as the refrigerant gas 181.

The heat absorber 309 of the refrigerant circuit 305 is disposed in the storage space 302. Cooling heat of the heat absorber 309 is stirred by the unshown air feeder so as to circulate inside the storage space 302 as indicated by dashed arrow in FIG. 4 . In this manner, the inside of the storage space 302 is cooled.

As described above, the refrigerator-freezer according to Embodiment 2 includes the above-described refrigerant compressor 100 according to Embodiment 1. In the refrigerant compressor 100 according to the present disclosure, as previously described, the thrust bearing is provided on the thrust surface 136 of the main bearing 134, and when the distance L between the center axis of the compression chamber 133 and the sliding surface lower end 139 (the second end at the far side from the compression chamber 133) of the main bearing 134 is in the range of 38 mm to 51 mm, the distance La between the center axis of the compression chamber 133 and the sliding surface upper end 138 (the first end adjacent to the compression chamber 133) of the main bearing 134 is less than or equal to 16 mm.

The above-described configuration of the refrigerant compressor 100 according to the present disclosure makes it possible to avoid increase in the overall height of the refrigerant compressor 100 without making the flange 128 thin, the flange 128 contributing to the stability of the eccentric shaft 122, and also makes it possible to reduce the load on the main shaft 124 without subjecting the sliding surfaces to special treatment. Consequently, the efficiency of the refrigerant compressor 100 can be further heightened without increasing the overall height of the refrigerant compressor 100. Therefore, by including the refrigerant compressor 100 having such advantages in the refrigerator-freezer, the power consumption of the refrigerator-freezer can be reduced, and also, the refrigerator-freezer can be made highly reliable.

EXAMPLES

Hereinafter, a more specific description of the present invention is given based on Examples and Comparative Example. However, the present invention is not limited by the description below. A person skilled in the art can make various changes, modifications, and alterations without departing from the scope of the present invention.

Example 1

As previously described, in the present disclosure, the main shaft load F on the refrigerant compressor 100 can be calculated based on the equation (2) shown below. As previously described, Fa in the equation (2) is a load from the piston 140 (piston load Fa); La is the distance between the center axis of the compression chamber 133 and the sliding surface upper end 138; and L is the distance between the center axis of the compression chamber 133 and the sliding surface lower end 139.

F=Fa×{1+La/(L−La)}  (2)

In the Examples, a reciprocating compressor (product name TKD91E manufactured by Panasonic Corporation) was assumed as the refrigerant compressor 100 (hereinafter, “the refrigerant compressor 100 of Example”). Then, based on the above equation (2), changes in the main shaft load F occurring when the distance La was changed within the range of 10 mm to 20 mm were compared with results of simulation of the inclination angle of the eccentric shaft 122 at the time of application of the piston load Fa. The comparison results are shown in a graph of FIG. 5 .

In the graph of FIG. 5 , the changes in the main shaft load F are indicated by solid line, and changes in the inclination angle of the eccentric shaft 122 are indicated by dotted line. Further, in the graph of FIG. 5 , the horizontal axis represents changes in the distance La (in units of mm), and the vertical axis represents changes in the main shaft load F (relative value) or changes in the inclination angle of the eccentric shaft 122 (relative value). The simulation of the inclination angle of the eccentric shaft 122 was performed by using CAE (computer aided engineering) software (NX series manufactured by Siemens PLM Software), which is commercially available structural analysis software.

As is clear from the correlation graph of FIG. 5 , since the main shaft load F is expressed by the equation (2), the main shaft load F increases in accordance with increase in the distance La. If the distance La is reduced without changing the distance L, the thickness of the flange 128 is inevitably reduced (i.e., the flange 128 inevitably gets thinner). When the flange 128 gets thinner, the eccentric shaft 122 gets inclined relative to the main shaft 124. Therefore, as shown in FIG. 5 , the inclination angle of the eccentric shaft 122 receiving the piston load Fa increases in accordance with reduction in the distance La.

In the refrigerant compressor 100, the piston 140 is coupled to the eccentric shaft 122 via the coupler 142, and the piston 140 is inserted in the compression chamber 133. If the inclination angle of the eccentric shaft 122 becomes excessively great, the orientation of the piston 140 coupled to the eccentric shaft 122 deteriorates. If the orientation of the piston 140 deteriorates while the refrigerant compressor 100 is operating, for example, wear occurs between the cylinder 132 and the piston 140, and consequently, there is a risk that sufficient reliability of the refrigerant compressor 100 cannot be secured.

Meanwhile, when the distance La is great, even in a state where the piston load Fa is applied, the inclination angle of the eccentric shaft 122 is asymptotically close to a predetermined value and does not change much. In such a case where the inclination angle can be assumed to be substantially constant at a predetermined value, it can be said that the piston 140 coupled to the eccentric shaft 122 is in a favorable orientation while the refrigerant compressor 100 is operating. Therefore, it is considered that favorable reliability of the refrigerant compressor 100 can be secured.

Based on the results shown in FIG. 5 , the correlation between the changes in the main shaft load F and the changes in the inclination angle of the eccentric shaft 122 can be divided into a region I, a region II, and a region III as shown in FIG. 5 .

In the region I, sufficient reliability of the refrigerant compressor 100 can be secured since the inclination angle of the eccentric shaft 122 is small. However, it is considered that the efficiency of the refrigerant compressor 100 is not sufficiently high in the region I since the main shaft load F is great.

In the region II, although the inclination angle of the eccentric shaft 122 is relatively greater than in the region I, sufficient reliability of the refrigerant compressor 100 can be secured. In addition, in the region II, since the main shaft load F can be made relatively smaller than in the region I, high efficiency of the refrigerant compressor 100 can be achieved.

In the region III, since the main shaft load F is smaller than in the region II, high efficiency of the refrigerant compressor 100 can be achieved. In the region III, however, since the inclination angle of the eccentric shaft 122 is greater than in the region II, depending on various conditions, there is a risk that sufficient reliability of the refrigerant compressor 100 cannot be secured.

As described above, according to the results shown in FIG. 5 , in order to both secure reliability and achieve high efficiency of the refrigerant compressor 100 according to the present disclosure, the region I where high efficiency of the refrigerant compressor 100 cannot be achieved is excluded from the correlation between the changes in the main shaft load F and the changes in the inclination angle of the eccentric shaft 122. Therefore, the upper limit of the distance La can be set to 16 mm.

Also, in the region III, depending on various conditions, it is possible that sufficient reliability of the refrigerant compressor 100 cannot be secured. Therefore, the region II is considered as a suitable range. Therefore, a preferable range of the distance La can be set to 12 mm to 16 m (12 mm≤La≤16 mm).

Example 2

In the refrigerant compressor 100 of Example (see Example 1), the distance La was set to 15.8 mm, and low-viscosity mineral oil having a mass molecular weight of greater than or equal to 500 and containing the high molecular weight component was used as the lubricating oil 180 (the above-described suitable lubricating oil; hereinafter, “the lubricating oil 180 of Example”). Specifically, the lubricating oil 180 of Example has a kinematic viscosity of 2.7 mm²/S at 40° C., and each of the principal component and the high molecular weight component of the lubricating oil 180 of Example is mineral oil.

The molecular weight distribution of the lubricating oil 180 containing 2.0% by mass of the high molecular weight component was measured by GPC technique. The measurement results are shown in FIG. 6A. In the molecular weight distribution graph of FIG. 6A, the vertical axis represents differential molar mass distribution (dW/d log M) and the horizontal axis represents mass molecular weight. The GPC technique was performed under the following conditions: a differential refractive index detector RI was used as a detector; a column having a diameter of 6.0 mm and a length of 15 cm was used; tetrahydrofuran (THF) was used as a solvent; monodispersed polystyrene was used as a standard sample; a flow velocity was set to 0.45 mL/min; and a column temperature was set to 40° C.

A shown in FIG. 6A, a peak of the principal component having a relatively low molecular weight, and a peak of the high molecular weight component indicated by block arrow, are observed in the lubricating oil 180 of Example. Although not illustrated, since conventional lubricating oil does not contain the high molecular weight component, no peak of the high molecular weight component is observed in the conventional lubricating oil.

The content of the high molecular weight component in the lubricating oil 180 of Example was changed over the range of 0% by mass to about 8% by mass, and the coefficient of performance of the refrigerant compressor 100 was evaluated. The evaluation results are shown in FIG. 6 . In the graph of FIG. 6B, the vertical axis represents the coefficient of performance, and the horizontal axis represents the content of the high molecular weight component. The coefficient of performance (COP) is the ratio of refrigeration capacity to energy consumption (input) (i.e., refrigeration capacity/input).

In the refrigerant compressor 100 in which the lubricating oil 180 of Example is used, it is understood from the results shown in FIG. 6B that the coefficient of performance can be favorably reduced by containing at least 0.5% by mass of the high molecular weight component in the lubricating oil 180.

Example 3

In the refrigerant compressor 100 of Example (see Example 1), the distance La was set to 15.8 mm similar to Example 2, and conventional lubricating oil (trade name FREOL S3 manufactured by JXTG Nippon Oil & Energy Corporation) was used as the lubricating oil 180. The coefficient of performance of the refrigerant compressor 100 was evaluated in the same manner as Example 2, with the operating rotation speed of the refrigerant compressor 100 being changed to 37 rps, 27 rps, and 17 rps. The evaluation results are indicated by square symbols in a graph of FIG. 7 . In the graph of FIG. 7 , the vertical axis represents the coefficient of performance (relative value), and the horizontal axis represents the operating rotation speed (in units of rps) of the refrigerant compressor.

Example 4

In the refrigerant compressor 100 of Example (see Example 1), the distance La was set to 15.8 mm similar to Example 2, and the suitable lubricating oil having a kinematic viscosity of 2.7 mm²/S at 40° C. and containing 2.0% by mass of the high molecular weight component (see Example 2 and FIG. 6A) was used as the lubricating oil 180. Except these, the coefficient of performance was evaluated in the same manner as Example 3. The evaluation results are indicated by triangle symbols in the graph of FIG. 7 .

Comparative Example

As a refrigerant compressor of Comparative Example, a conventional refrigerant compressor was used, in which the distance La was set to greater than 16 mm and conventional lubricating oil was used similar to Example 3. Except these, the coefficient of performance was evaluated in the same manner as Example 3. The evaluation results are indicated by circle symbols in the graph of FIG. 7 .

Comparison of Examples 3, 4, and Comparative Example

It is understood from FIG. 7 that, at least, at an operating rotation speed of 35 rps or less, the coefficient of performance (i.e., compressor efficiency) of the refrigerant compressors 100 of Examples 3 and 4 is significantly increased compared to the conventional refrigerant compressor of Comparative Example. It is understood from the comparison of Comparative Example and Example 3 that, from 27 rps, there is a tendency for the difference in coefficient of performance between Comparative Example and Example 3 to increase in accordance with decrease in the operating rotation speed.

Further, it is understood from the comparison of Example 3 and Example 4 that the coefficient of performance is further increased by using, as the lubricating oil 180, not the conventional lubricating oil (Example 3) but the low-viscosity lubricating oil containing the high molecular weight component (Example 4). In particular, from the comparison of Example 3 and Example 4, it is understood that, from 27 rps, the difference in coefficient of performance between Example 3 and Example 4 further increases in accordance with decrease in the operating rotation speed.

It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims. Embodiments obtained by suitably combining technical means that are disclosed in different embodiments and variations also fall within the technical scope of the present invention.

From the foregoing description, numerous modifications and other embodiments of the present invention are obvious to those skilled in the art. Accordingly, the foregoing description is to be construed as illustrative only, and is provided for the purpose of teaching those skilled in the art the best mode for carrying out the present invention. The structural and/or functional details may be substantially modified without departing from the scope of the present invention.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, the efficiency of a hermetic refrigerant compressor can be improved while maintaining high reliability of the hermetic refrigerant compressor. Therefore, the present invention is widely applicable to various equipment that uses a refrigeration cycle.

REFERENCE SIGNS LIST

100: hermetic refrigerant compressor

102: sealed container

104: electric element

106: compression element

108: compressor body

120: crankshaft

122: eccentric shaft

124: main shaft

125: oil feeding mechanism

126: sliding surface

127: non-sliding surface

128: flange

130: cylinder block

132: cylinder

133: compression chamber

134 main bearing

136: thrust surface

137: tubular extension

138: sliding surface upper end (first end)

139: sliding surface lower end (second end)

140: piston

142: coupler

150: stator

152: rotor

180: lubricating oil

181: refrigerant gas

190: suspension spring

202: upper race

204: ball (rolling element)

205: retainer

206: lower race

210: thrust ball bearing (thrust bearing)

301: body

302: storage space

303: machinery room

304: dividing wall

305: refrigerant circuit

307: radiator

308: decompressor

309: heat absorber 

1. A hermetic refrigerant compressor comprising a sealed container in which lubricating oil is stored, the sealed container accommodating an electric element and a compression element, the compression element being driven by the electric element and configured to compress a refrigerant, wherein the compression element includes: a crankshaft including a main shaft and an eccentric shaft; a cylinder block including a compression chamber; a piston that is inserted in the compression chamber in a reciprocable manner; a coupler that couples the piston and the eccentric shaft; a main bearing that pivotally supports the main shaft; and a thrust bearing provided on a thrust surface of the main bearing, one end of a sliding surface of the main bearing, the one end being closer to the compression chamber than an opposite end of the sliding surface, is a first end, the opposite end of the sliding surface is a second end, a distance between a center axis of the compression chamber and the second end of the sliding surface of the main bearing is a distance L, a distance between the center axis of the compression chamber and the first end of the sliding surface of the main bearing is a distance La, and when the distance L is in a range of 38 mm to 51 mm, the distance La is less than or equal to 16 mm.
 2. The hermetic refrigerant compressor according to claim 1, wherein the thrust bearing includes: a lower race positioned on the thrust surface; an upper race positioned facing the lower race; and a plurality of rolling elements that are arranged between the upper and lower races and that are rollably in contact with the upper and lower races, and the rolling elements are balls.
 3. The hermetic refrigerant compressor according to claim 1, wherein the lubricating oil has a kinematic viscosity in a range of 1 mm²/S to 7 mm²/S at 40° C.
 4. The hermetic refrigerant compressor according to claim 3, wherein the lubricating oil has a mass average molecular weight in a range of 150 to 400, and contains 0.5% by mass or more of a high molecular weight component, and the high molecular weight component has a mass molecular weight of greater than or equal to
 500. 5. The hermetic refrigerant compressor according to claim 1, wherein the lubricating oil contains an oiliness agent.
 6. The hermetic refrigerant compressor according to claim 5, wherein the oiliness agent is an ester-based compound.
 7. The hermetic refrigerant compressor according to claim 1, wherein a distillation fraction of the lubricating oil at a distillation temperature of 300° C. is 0.1% or greater, and a distillation end point is 440° C. or higher.
 8. The hermetic refrigerant compressor according to claim 1, wherein the lubricating oil contains a sliding modifier such that a content of the sliding modifier in the lubricating oil in terms of an atomic weight of sulfur is greater than or equal to 100 ppm.
 9. The hermetic refrigerant compressor according to claim 1, wherein the lubricating oil contains a phosphorus-based extreme-pressure additive.
 10. The hermetic refrigerant compressor according to claim 1, wherein the lubricating oil is at least one selected from the group consisting of mineral oil, alkyl benzene oil, and ester oil.
 11. The hermetic refrigerant compressor according to claim 1, wherein the electric element is inverter-driven at a plurality of operating frequencies.
 12. The hermetic refrigerant compressor according to claim 11, wherein the hermetic refrigerant compressor is operated at a rotation speed of 35 rps or less.
 13. A refrigerator-freezer comprising a refrigerant circuit including: the hermetic refrigerant compressor according to claim 1; a radiator; a decompressor; and a heat absorber, wherein in the refrigerant circuit, the hermetic refrigerant compressor, the radiator, the decompressor, and the heat absorber are connected by piping in an annular manner. 